Interquartile Mean (IQM)

1

Where can I find javascript to obtain the interquartile mean of an array of numbers?

2

Here’s a modification of an implementation from the “code golf” stackexchange:

function IQM (arr) {
  const l = arr.length;
  return arr.concat(arr,arr,arr)
    .sort((x,y) => x-y)
    .slice(l, -l)
    .reduce((a,v) => a+v, 0)/(2*l);
}

The idea is to concatenate 3 copies of the original array arr so that one has a “quadruplicated” array. Then one sorts and slices to get (a quadruplication of) the middle quartiles (an array of length 2*l, where l=arr.length). Finally, one computes the mean.

Here’s Neil’s original code:

a=>a.concat(a,a,a).sort(g=(x,y)=>x-y).slice(l=a.length,-l).reduce(g,0)/l/-2
2 Likes
3

Wonderful and quick reply. Fresh, smart, and surprising, too. Thanks.

4

There is also a package available on npm: compute-midmean.

5

In the unlikely case it matters, note that this npm package treats arrays with lengths not divisible by 4 in a different way than the code I copied from stackexchange does.

The latter calculation gives fractional weights to “in-between” values as is done on Wikipedia, whereas compute-midmean gives them a full weight (which follows the paper that they cite).

6

Thanks! For now, the one-liner suffices, and I find it quite elegant (despite the array quadruplication).

The difference in calculation does not make much difference for me. I just want to strip any outliers from the set.